The objective of the proposed research is to develop clinically applicable DNA microarray methods for detecting chromosome imbalance (e.g. aneuploidy) in isolated cells. Such tests will be widely applicable and we anticipate their use in several areas: 1) non-invasive prenatal testing based on the analysis of small numbers of fetal cells isolated from the maternal circulation; 2) cancer research, specifically the analysis of tumor cells harvested from the blood stream, body cavity, or by laser capture microdissection; 3) preimplantation genetic diagnosis (PGD) and in vitro fertilization (IVF), the area addressed in detail in this proposal. Currently, IVF is a relatively inefficient procedure, the majority of patients requiring two or more cycles to achieve a pregnancy. Couples that require multiple cycles endure significant emotional, physical and financial demands. To improve pregnancy rates many IVF clinics replace multiple embryos each cycle. However, this practice has often led to high order pregnancies (triplets, etc) and result in increased risk of congenital abnormality for the children and health risks for the mother. It is now known that >30% of human oocytes and >50% of human preimplantation embryos are aneuploid. Preimplantation embryos affected by lethal chromosome abnormalities are frequently morphologically normal and are often inadvertently transferred during IVF, leading to implantation failure or spontaneous abortion. Preimplantation screening of polar bodies (PBs) biopsied from oocytes allows normal oocytes to be identified and the resulting embryos preferentially transferred to the mother. This has been shown to lead to improved IVF success rates for several patient groups, including women >35 years, translocation carriers, and couples with a history of repeated miscarriage. Unfortunately current PGD techniques, which rely on fluorescence in situ hybridization (FISH) analysis of PBs or embryo cells, are only capable of detecting approximately 1/3 of the human chromosomes and consequently many oocytes carrying lethal abnormalities are not detected. We propose the development of a new diagnostic method utilizing DNA microarray technology and building on our pioneering work with whole genome amplification and comparative genomic hybridization. We will create a product that will allow every chromosome to be analyzed in single cells, in a manner compatible with transfer to IVF clinics that have little scientific know-how. The detection and avoidance of all aneuploid oocytes will lead to improved IVF outcomes for thousands of patients. Multiple births might also be reduced a s increased IVF success rates mean that fewer embryos need be transferred.